Three-dimensional parts are typically machined using a molded block of material as a starting point. Casting the block of material is a relatively cost efficient and accurate process, although forming the final part using post-casting machining and retooling processes can be long and expensive.
A more sophisticated method for manufacturing parts is commonly called rapid prototyping. Rapid prototyping involves producing computer models of a three-dimensional object and corresponding two-dimensional cross sections of the object. The models are stored in a memory as a computer aided design (CAD) file. The computer transmits signals from the memory to manufacturing equipment that responds to the signals and builds layer-by-layer until the three-dimensional object is produced. Building by adding material where it is needed instead of removing material where it is not needed is an efficient process that eliminates the need for retooling and post-mold machining. Further, rapid prototyping is capable of producing complex structures. However, rapid prototyping has typically been used to produce plastic parts, and there are few techniques for successfully manufacturing parts incorporating metals.
One rapid prototyping process uses selective laser sintering (SLS) for locally melting, solidifying and adhering polymers that form the three-dimensional object, both in an intralayer and an interlayer sense. An SLS process uses a laser to sinter a powder and form a coherent mass therefrom. Rockwell Scientific Company and Boeing-Rocketdyne have successfully developed methods that incorporate SLS processes for fabrication of nickel-based alloys and iron-based alloys, and these methods are disclosed in U.S. Pat. Nos. 5,932,055 and 5,745,834. The methods are known as direct metal fabrication (DMF) methods and include two-steps. First, a green part is formed using an SLS process to selectively sinter polymer binders and thereby bind a powdered metal alloy. After the so-called green part is formed, it is furnace treated to remove the polymer binders and to liquid phase sinter the powder metal part to full density.
During the SLS stage of the DMF method the polymer binder includes nylon 12 and bismaleimide (BMI), and a melting temperature depressant such as boron is utilized during the latter liquid phase sintering step. Although these binders are effective for binding some metal powders, they are unable to effectively bind powdered build material containing titanium or titanium alloys. Polymer binders leave a significant carbon residue that causes titanium parts to be brittle, and consequently ineffective. Also, boron does not have the desired eutectic behavior for enhancing the liquid phase sintering step with titanium alloys.
Other methods for building titanium alloy parts directly from a CAD file using powdered build material utilizes direct laser deposition technology such as laser engineered net shaping (LENS by Optomec®) and laser forming (Aeromet®). However, neither method is able to build intricate, discontinuous surfaces such as net shaped structures on the parts. Also, internal cavities and channels are virtually impossible to form due to lack of support during the building process.
Accordingly, it is desirable to provide a method for fabricating parts made of titanium or titanium alloys. In addition, it is desirable to provide such a method that is inexpensive and efficient. Furthermore, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.